1. Field of the Invention
The present invention concerns a high-density and high-capacity distribution frame, in particular for optical fibers, used as an optical distribution frame for user optical fibers, or as a sub-distribution frame.
2. Description of the Prior Art
An optical distribution frame is a device essentially assuring optical continuity in a way that is totally flexible and can be modified between ends of first optical fibers, for example optical fibers of underground network cables, and ends of second optical fibers, for example fibers coming from user equipments of a telephone central office. The distribution frame therefore enables unlimited fiber-to-fiber modification of the assignments between first fibers and second fibers defined at the time of initial wiring (cross-connect function) and cancelling such assignments temporarily or permanently (delay function), on a fiber by fiber basis. In the context of expanding use of fiber optics in distribution networks, it has become necessary to design high-capacity optical distribution frames and to achieve densities in optical technology comparable with those already achieved in traditional distribution frames for copper telephone lines.
In a matrix architecture optical distribution frame connection modules, also known as connectors, are arranged in a plane matrix. The ends of the first optical fibers are fed in through one of faces of the distribution frame in a fixed manner. The ends of the second optical fibers can be moved over the other face of the matrix distribution frame during cross-connection operations (NTT Japanese patent applications Nos. 07-318,820, 07-244,225, 07-333,530 and 07-333,531).
There are two variants of matrix distribution frames, a single-stage variant and a two-stage variant.
In the single-stage variant the first fibers, which are network fibers, for example, are fed to one face of the matrix and the second fibers, which are fibers from user equipments, for example, are fed to the other face of the matrix. During cross-connection operations the ends of either the network fibers or the equipment fibers are mobile; in other words they can be withdrawn from the connection modules and inserted into them.
In the two-stage variant the stages are two matrices. One face of each matrix receives the network fibers or the user equipment fibers. Optical continuity between the network fibers and the equipment fibers is assured by separate fibers, known as connecting fibers, disposed between the two matrices. The connecting fibers are moved during cross-connection operations.
The connection matrix can be associated with an organization panel or an alignment strip which organizes the optical fibers reaching the face of the matrix in a spatial manner that cannot be changed, regardless of subsequent cross-connection operations. The panel includes a matrix of holes through which respective optical fibers pass. The movements of optical fibers associated with cross-connection operations and the associated crossovers of the fibers take place between the organization panel and the connection module matrix.
A cross-connection operation is essentially effected by carrying out three basic operations in succession:
disconnecting one optical fiber end in a connection module at the face of the matrix; PA1 extracting the optical fiber from the organization panel by pulling it through the mass of crossing fibers between the connection module matrix and the organization panel, the function of the latter being to enable identification of the optical fibers to be extracted; and PA1 pulling the optical fiber extracted from the organization panel towards the connection module to be connected, passing it over the existing mass of crossing optical fibers.
In these prior art distribution frames the matrix organization of the connection modules makes access to them difficult, since to reach a connection module it is necessary to thread the hand or a tool through the curtain formed by the fiber ends terminating at the matrix. This operation is even more difficult if the density of connection modules is high. This "infiltration" through the curtain of fiber ends is also necessary for carrying out maintenance on the connection modules.
Furthermore, the presence of the organization panel makes it necessary to pull an optical fiber to be disconnected or disconnected/connected through all of the mass of optical fibers between the matrix and the organization panel, and then to pull another optical fiber from and through the organization panel, if necessary, and then across all the other surrounding optical fibers between the panel and the matrix. As the fibers are neither changed nor trimmed in length during cross-connection, they must be sufficiently long to enable the fiber ends to be connected to near and far away connection modules in the matrix.
In the case of a low-density distribution frame the connecting optical fibers often have highly disparate and excessive lengths, which rules out interchanging connection optical fibers during cross-connection operations. This disparity is more serious if the connection modules are relatively widely spaced from each other, i.e. if their density is relatively low, and if the matrices have increasingly large dimensions in order to increase their capacity.